Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 881 insertions, 0 deletions

diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
new file mode 100644
index 000000000..c6ea2903c
--- /dev/null
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -0,0 +1,881 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+/*
+ * Copyright (c) 2016-2018 Oracle. All rights reserved.
+ * Copyright (c) 2014 Open Grid Computing, Inc. All rights reserved.
+ * Copyright (c) 2005-2006 Network Appliance, Inc. All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the BSD-type
+ * license below:
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *      Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *
+ *      Redistributions in binary form must reproduce the above
+ *      copyright notice, this list of conditions and the following
+ *      disclaimer in the documentation and/or other materials provided
+ *      with the distribution.
+ *
+ *      Neither the name of the Network Appliance, Inc. nor the names of
+ *      its contributors may be used to endorse or promote products
+ *      derived from this software without specific prior written
+ *      permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Author: Tom Tucker <tom@opengridcomputing.com>
+ */
+
+/* Operation
+ *
+ * The main entry point is svc_rdma_recvfrom. This is called from
+ * svc_recv when the transport indicates there is incoming data to
+ * be read. "Data Ready" is signaled when an RDMA Receive completes,
+ * or when a set of RDMA Reads complete.
+ *
+ * An svc_rqst is passed in. This structure contains an array of
+ * free pages (rq_pages) that will contain the incoming RPC message.
+ *
+ * Short messages are moved directly into svc_rqst::rq_arg, and
+ * the RPC Call is ready to be processed by the Upper Layer.
+ * svc_rdma_recvfrom returns the length of the RPC Call message,
+ * completing the reception of the RPC Call.
+ *
+ * However, when an incoming message has Read chunks,
+ * svc_rdma_recvfrom must post RDMA Reads to pull the RPC Call's
+ * data payload from the client. svc_rdma_recvfrom sets up the
+ * RDMA Reads using pages in svc_rqst::rq_pages, which are
+ * transferred to an svc_rdma_recv_ctxt for the duration of the
+ * I/O. svc_rdma_recvfrom then returns zero, since the RPC message
+ * is still not yet ready.
+ *
+ * When the Read chunk payloads have become available on the
+ * server, "Data Ready" is raised again, and svc_recv calls
+ * svc_rdma_recvfrom again. This second call may use a different
+ * svc_rqst than the first one, thus any information that needs
+ * to be preserved across these two calls is kept in an
+ * svc_rdma_recv_ctxt.
+ *
+ * The second call to svc_rdma_recvfrom performs final assembly
+ * of the RPC Call message, using the RDMA Read sink pages kept in
+ * the svc_rdma_recv_ctxt. The xdr_buf is copied from the
+ * svc_rdma_recv_ctxt to the second svc_rqst. The second call returns
+ * the length of the completed RPC Call message.
+ *
+ * Page Management
+ *
+ * Pages under I/O must be transferred from the first svc_rqst to an
+ * svc_rdma_recv_ctxt before the first svc_rdma_recvfrom call returns.
+ *
+ * The first svc_rqst supplies pages for RDMA Reads. These are moved
+ * from rqstp::rq_pages into ctxt::pages. The consumed elements of
+ * the rq_pages array are set to NULL and refilled with the first
+ * svc_rdma_recvfrom call returns.
+ *
+ * During the second svc_rdma_recvfrom call, RDMA Read sink pages
+ * are transferred from the svc_rdma_recv_ctxt to the second svc_rqst
+ * (see rdma_read_complete() below).
+ */
+
+#include <linux/spinlock.h>
+#include <asm/unaligned.h>
+#include <rdma/ib_verbs.h>
+#include <rdma/rdma_cm.h>
+
+#include <linux/sunrpc/xdr.h>
+#include <linux/sunrpc/debug.h>
+#include <linux/sunrpc/rpc_rdma.h>
+#include <linux/sunrpc/svc_rdma.h>
+
+#include "xprt_rdma.h"
+#include <trace/events/rpcrdma.h>
+
+#define RPCDBG_FACILITY	RPCDBG_SVCXPRT
+
+static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc);
+
+static inline struct svc_rdma_recv_ctxt *
+svc_rdma_next_recv_ctxt(struct list_head *list)
+{
+	return list_first_entry_or_null(list, struct svc_rdma_recv_ctxt,
+					rc_list);
+}
+
+static void svc_rdma_recv_cid_init(struct svcxprt_rdma *rdma,
+				   struct rpc_rdma_cid *cid)
+{
+	cid->ci_queue_id = rdma->sc_rq_cq->res.id;
+	cid->ci_completion_id = atomic_inc_return(&rdma->sc_completion_ids);
+}
+
+static struct svc_rdma_recv_ctxt *
+svc_rdma_recv_ctxt_alloc(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_recv_ctxt *ctxt;
+	dma_addr_t addr;
+	void *buffer;
+
+	ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
+	if (!ctxt)
+		goto fail0;
+	buffer = kmalloc(rdma->sc_max_req_size, GFP_KERNEL);
+	if (!buffer)
+		goto fail1;
+	addr = ib_dma_map_single(rdma->sc_pd->device, buffer,
+				 rdma->sc_max_req_size, DMA_FROM_DEVICE);
+	if (ib_dma_mapping_error(rdma->sc_pd->device, addr))
+		goto fail2;
+
+	svc_rdma_recv_cid_init(rdma, &ctxt->rc_cid);
+
+	ctxt->rc_recv_wr.next = NULL;
+	ctxt->rc_recv_wr.wr_cqe = &ctxt->rc_cqe;
+	ctxt->rc_recv_wr.sg_list = &ctxt->rc_recv_sge;
+	ctxt->rc_recv_wr.num_sge = 1;
+	ctxt->rc_cqe.done = svc_rdma_wc_receive;
+	ctxt->rc_recv_sge.addr = addr;
+	ctxt->rc_recv_sge.length = rdma->sc_max_req_size;
+	ctxt->rc_recv_sge.lkey = rdma->sc_pd->local_dma_lkey;
+	ctxt->rc_recv_buf = buffer;
+	ctxt->rc_temp = false;
+	return ctxt;
+
+fail2:
+	kfree(buffer);
+fail1:
+	kfree(ctxt);
+fail0:
+	return NULL;
+}
+
+static void svc_rdma_recv_ctxt_destroy(struct svcxprt_rdma *rdma,
+				       struct svc_rdma_recv_ctxt *ctxt)
+{
+	ib_dma_unmap_single(rdma->sc_pd->device, ctxt->rc_recv_sge.addr,
+			    ctxt->rc_recv_sge.length, DMA_FROM_DEVICE);
+	kfree(ctxt->rc_recv_buf);
+	kfree(ctxt);
+}
+
+/**
+ * svc_rdma_recv_ctxts_destroy - Release all recv_ctxt's for an xprt
+ * @rdma: svcxprt_rdma being torn down
+ *
+ */
+void svc_rdma_recv_ctxts_destroy(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_recv_ctxt *ctxt;
+	struct llist_node *node;
+
+	while ((node = llist_del_first(&rdma->sc_recv_ctxts))) {
+		ctxt = llist_entry(node, struct svc_rdma_recv_ctxt, rc_node);
+		svc_rdma_recv_ctxt_destroy(rdma, ctxt);
+	}
+}
+
+static struct svc_rdma_recv_ctxt *
+svc_rdma_recv_ctxt_get(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_recv_ctxt *ctxt;
+	struct llist_node *node;
+
+	node = llist_del_first(&rdma->sc_recv_ctxts);
+	if (!node)
+		goto out_empty;
+	ctxt = llist_entry(node, struct svc_rdma_recv_ctxt, rc_node);
+
+out:
+	ctxt->rc_page_count = 0;
+	ctxt->rc_read_payload_length = 0;
+	return ctxt;
+
+out_empty:
+	ctxt = svc_rdma_recv_ctxt_alloc(rdma);
+	if (!ctxt)
+		return NULL;
+	goto out;
+}
+
+/**
+ * svc_rdma_recv_ctxt_put - Return recv_ctxt to free list
+ * @rdma: controlling svcxprt_rdma
+ * @ctxt: object to return to the free list
+ *
+ */
+void svc_rdma_recv_ctxt_put(struct svcxprt_rdma *rdma,
+			    struct svc_rdma_recv_ctxt *ctxt)
+{
+	unsigned int i;
+
+	for (i = 0; i < ctxt->rc_page_count; i++)
+		put_page(ctxt->rc_pages[i]);
+
+	if (!ctxt->rc_temp)
+		llist_add(&ctxt->rc_node, &rdma->sc_recv_ctxts);
+	else
+		svc_rdma_recv_ctxt_destroy(rdma, ctxt);
+}
+
+/**
+ * svc_rdma_release_rqst - Release transport-specific per-rqst resources
+ * @rqstp: svc_rqst being released
+ *
+ * Ensure that the recv_ctxt is released whether or not a Reply
+ * was sent. For example, the client could close the connection,
+ * or svc_process could drop an RPC, before the Reply is sent.
+ */
+void svc_rdma_release_rqst(struct svc_rqst *rqstp)
+{
+	struct svc_rdma_recv_ctxt *ctxt = rqstp->rq_xprt_ctxt;
+	struct svc_xprt *xprt = rqstp->rq_xprt;
+	struct svcxprt_rdma *rdma =
+		container_of(xprt, struct svcxprt_rdma, sc_xprt);
+
+	rqstp->rq_xprt_ctxt = NULL;
+	if (ctxt)
+		svc_rdma_recv_ctxt_put(rdma, ctxt);
+}
+
+static int __svc_rdma_post_recv(struct svcxprt_rdma *rdma,
+				struct svc_rdma_recv_ctxt *ctxt)
+{
+	int ret;
+
+	trace_svcrdma_post_recv(ctxt);
+	ret = ib_post_recv(rdma->sc_qp, &ctxt->rc_recv_wr, NULL);
+	if (ret)
+		goto err_post;
+	return 0;
+
+err_post:
+	trace_svcrdma_rq_post_err(rdma, ret);
+	svc_rdma_recv_ctxt_put(rdma, ctxt);
+	return ret;
+}
+
+static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_recv_ctxt *ctxt;
+
+	if (test_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags))
+		return 0;
+	ctxt = svc_rdma_recv_ctxt_get(rdma);
+	if (!ctxt)
+		return -ENOMEM;
+	return __svc_rdma_post_recv(rdma, ctxt);
+}
+
+/**
+ * svc_rdma_post_recvs - Post initial set of Recv WRs
+ * @rdma: fresh svcxprt_rdma
+ *
+ * Returns true if successful, otherwise false.
+ */
+bool svc_rdma_post_recvs(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_recv_ctxt *ctxt;
+	unsigned int i;
+	int ret;
+
+	for (i = 0; i < rdma->sc_max_requests; i++) {
+		ctxt = svc_rdma_recv_ctxt_get(rdma);
+		if (!ctxt)
+			return false;
+		ctxt->rc_temp = true;
+		ret = __svc_rdma_post_recv(rdma, ctxt);
+		if (ret)
+			return false;
+	}
+	return true;
+}
+
+/**
+ * svc_rdma_wc_receive - Invoked by RDMA provider for each polled Receive WC
+ * @cq: Completion Queue context
+ * @wc: Work Completion object
+ *
+ * NB: The svc_xprt/svcxprt_rdma is pinned whenever it's possible that
+ * the Receive completion handler could be running.
+ */
+static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
+{
+	struct svcxprt_rdma *rdma = cq->cq_context;
+	struct ib_cqe *cqe = wc->wr_cqe;
+	struct svc_rdma_recv_ctxt *ctxt;
+
+	/* WARNING: Only wc->wr_cqe and wc->status are reliable */
+	ctxt = container_of(cqe, struct svc_rdma_recv_ctxt, rc_cqe);
+
+	trace_svcrdma_wc_receive(wc, &ctxt->rc_cid);
+	if (wc->status != IB_WC_SUCCESS)
+		goto flushed;
+
+	if (svc_rdma_post_recv(rdma))
+		goto post_err;
+
+	/* All wc fields are now known to be valid */
+	ctxt->rc_byte_len = wc->byte_len;
+	ib_dma_sync_single_for_cpu(rdma->sc_pd->device,
+				   ctxt->rc_recv_sge.addr,
+				   wc->byte_len, DMA_FROM_DEVICE);
+
+	spin_lock(&rdma->sc_rq_dto_lock);
+	list_add_tail(&ctxt->rc_list, &rdma->sc_rq_dto_q);
+	/* Note the unlock pairs with the smp_rmb in svc_xprt_ready: */
+	set_bit(XPT_DATA, &rdma->sc_xprt.xpt_flags);
+	spin_unlock(&rdma->sc_rq_dto_lock);
+	if (!test_bit(RDMAXPRT_CONN_PENDING, &rdma->sc_flags))
+		svc_xprt_enqueue(&rdma->sc_xprt);
+	return;
+
+flushed:
+post_err:
+	svc_rdma_recv_ctxt_put(rdma, ctxt);
+	set_bit(XPT_CLOSE, &rdma->sc_xprt.xpt_flags);
+	svc_xprt_enqueue(&rdma->sc_xprt);
+}
+
+/**
+ * svc_rdma_flush_recv_queues - Drain pending Receive work
+ * @rdma: svcxprt_rdma being shut down
+ *
+ */
+void svc_rdma_flush_recv_queues(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_recv_ctxt *ctxt;
+
+	while ((ctxt = svc_rdma_next_recv_ctxt(&rdma->sc_read_complete_q))) {
+		list_del(&ctxt->rc_list);
+		svc_rdma_recv_ctxt_put(rdma, ctxt);
+	}
+	while ((ctxt = svc_rdma_next_recv_ctxt(&rdma->sc_rq_dto_q))) {
+		list_del(&ctxt->rc_list);
+		svc_rdma_recv_ctxt_put(rdma, ctxt);
+	}
+}
+
+static void svc_rdma_build_arg_xdr(struct svc_rqst *rqstp,
+				   struct svc_rdma_recv_ctxt *ctxt)
+{
+	struct xdr_buf *arg = &rqstp->rq_arg;
+
+	arg->head[0].iov_base = ctxt->rc_recv_buf;
+	arg->head[0].iov_len = ctxt->rc_byte_len;
+	arg->tail[0].iov_base = NULL;
+	arg->tail[0].iov_len = 0;
+	arg->page_len = 0;
+	arg->page_base = 0;
+	arg->buflen = ctxt->rc_byte_len;
+	arg->len = ctxt->rc_byte_len;
+}
+
+/* This accommodates the largest possible Write chunk.
+ */
+#define MAX_BYTES_WRITE_CHUNK ((u32)(RPCSVC_MAXPAGES << PAGE_SHIFT))
+
+/* This accommodates the largest possible Position-Zero
+ * Read chunk or Reply chunk.
+ */
+#define MAX_BYTES_SPECIAL_CHUNK ((u32)((RPCSVC_MAXPAGES + 2) << PAGE_SHIFT))
+
+/* Sanity check the Read list.
+ *
+ * Implementation limits:
+ * - This implementation supports only one Read chunk.
+ *
+ * Sanity checks:
+ * - Read list does not overflow Receive buffer.
+ * - Segment size limited by largest NFS data payload.
+ *
+ * The segment count is limited to how many segments can
+ * fit in the transport header without overflowing the
+ * buffer. That's about 40 Read segments for a 1KB inline
+ * threshold.
+ *
+ * Return values:
+ *       %true: Read list is valid. @rctxt's xdr_stream is updated
+ *		to point to the first byte past the Read list.
+ *      %false: Read list is corrupt. @rctxt's xdr_stream is left
+ *		in an unknown state.
+ */
+static bool xdr_check_read_list(struct svc_rdma_recv_ctxt *rctxt)
+{
+	u32 position, len;
+	bool first;
+	__be32 *p;
+
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+
+	len = 0;
+	first = true;
+	while (xdr_item_is_present(p)) {
+		p = xdr_inline_decode(&rctxt->rc_stream,
+				      rpcrdma_readseg_maxsz * sizeof(*p));
+		if (!p)
+			return false;
+
+		if (first) {
+			position = be32_to_cpup(p);
+			first = false;
+		} else if (be32_to_cpup(p) != position) {
+			return false;
+		}
+		p += 2;
+		len += be32_to_cpup(p);
+
+		p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+		if (!p)
+			return false;
+	}
+	return len <= MAX_BYTES_SPECIAL_CHUNK;
+}
+
+/* The segment count is limited to how many segments can
+ * fit in the transport header without overflowing the
+ * buffer. That's about 60 Write segments for a 1KB inline
+ * threshold.
+ */
+static bool xdr_check_write_chunk(struct svc_rdma_recv_ctxt *rctxt, u32 maxlen)
+{
+	u32 i, segcount, total;
+	__be32 *p;
+
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+	segcount = be32_to_cpup(p);
+
+	total = 0;
+	for (i = 0; i < segcount; i++) {
+		u32 handle, length;
+		u64 offset;
+
+		p = xdr_inline_decode(&rctxt->rc_stream,
+				      rpcrdma_segment_maxsz * sizeof(*p));
+		if (!p)
+			return false;
+
+		xdr_decode_rdma_segment(p, &handle, &length, &offset);
+		trace_svcrdma_decode_wseg(handle, length, offset);
+
+		total += length;
+	}
+	return total <= maxlen;
+}
+
+/* Sanity check the Write list.
+ *
+ * Implementation limits:
+ * - This implementation currently supports only one Write chunk.
+ *
+ * Sanity checks:
+ * - Write list does not overflow Receive buffer.
+ * - Chunk size limited by largest NFS data payload.
+ *
+ * Return values:
+ *       %true: Write list is valid. @rctxt's xdr_stream is updated
+ *		to point to the first byte past the Write list.
+ *      %false: Write list is corrupt. @rctxt's xdr_stream is left
+ *		in an unknown state.
+ */
+static bool xdr_check_write_list(struct svc_rdma_recv_ctxt *rctxt)
+{
+	u32 chcount = 0;
+	__be32 *p;
+
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+	rctxt->rc_write_list = p;
+	while (xdr_item_is_present(p)) {
+		if (!xdr_check_write_chunk(rctxt, MAX_BYTES_WRITE_CHUNK))
+			return false;
+		++chcount;
+		p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+		if (!p)
+			return false;
+	}
+	if (!chcount)
+		rctxt->rc_write_list = NULL;
+	return chcount < 2;
+}
+
+/* Sanity check the Reply chunk.
+ *
+ * Sanity checks:
+ * - Reply chunk does not overflow Receive buffer.
+ * - Chunk size limited by largest NFS data payload.
+ *
+ * Return values:
+ *       %true: Reply chunk is valid. @rctxt's xdr_stream is updated
+ *		to point to the first byte past the Reply chunk.
+ *      %false: Reply chunk is corrupt. @rctxt's xdr_stream is left
+ *		in an unknown state.
+ */
+static bool xdr_check_reply_chunk(struct svc_rdma_recv_ctxt *rctxt)
+{
+	__be32 *p;
+
+	p = xdr_inline_decode(&rctxt->rc_stream, sizeof(*p));
+	if (!p)
+		return false;
+	rctxt->rc_reply_chunk = NULL;
+	if (xdr_item_is_present(p)) {
+		if (!xdr_check_write_chunk(rctxt, MAX_BYTES_SPECIAL_CHUNK))
+			return false;
+		rctxt->rc_reply_chunk = p;
+	}
+	return true;
+}
+
+/* RPC-over-RDMA Version One private extension: Remote Invalidation.
+ * Responder's choice: requester signals it can handle Send With
+ * Invalidate, and responder chooses one R_key to invalidate.
+ *
+ * If there is exactly one distinct R_key in the received transport
+ * header, set rc_inv_rkey to that R_key. Otherwise, set it to zero.
+ *
+ * Perform this operation while the received transport header is
+ * still in the CPU cache.
+ */
+static void svc_rdma_get_inv_rkey(struct svcxprt_rdma *rdma,
+				  struct svc_rdma_recv_ctxt *ctxt)
+{
+	__be32 inv_rkey, *p;
+	u32 i, segcount;
+
+	ctxt->rc_inv_rkey = 0;
+
+	if (!rdma->sc_snd_w_inv)
+		return;
+
+	inv_rkey = xdr_zero;
+	p = ctxt->rc_recv_buf;
+	p += rpcrdma_fixed_maxsz;
+
+	/* Read list */
+	while (xdr_item_is_present(p++)) {
+		p++;	/* position */
+		if (inv_rkey == xdr_zero)
+			inv_rkey = *p;
+		else if (inv_rkey != *p)
+			return;
+		p += 4;
+	}
+
+	/* Write list */
+	while (xdr_item_is_present(p++)) {
+		segcount = be32_to_cpup(p++);
+		for (i = 0; i < segcount; i++) {
+			if (inv_rkey == xdr_zero)
+				inv_rkey = *p;
+			else if (inv_rkey != *p)
+				return;
+			p += 4;
+		}
+	}
+
+	/* Reply chunk */
+	if (xdr_item_is_present(p++)) {
+		segcount = be32_to_cpup(p++);
+		for (i = 0; i < segcount; i++) {
+			if (inv_rkey == xdr_zero)
+				inv_rkey = *p;
+			else if (inv_rkey != *p)
+				return;
+			p += 4;
+		}
+	}
+
+	ctxt->rc_inv_rkey = be32_to_cpu(inv_rkey);
+}
+
+/**
+ * svc_rdma_xdr_decode_req - Decode the transport header
+ * @rq_arg: xdr_buf containing ingress RPC/RDMA message
+ * @rctxt: state of decoding
+ *
+ * On entry, xdr->head[0].iov_base points to first byte of the
+ * RPC-over-RDMA transport header.
+ *
+ * On successful exit, head[0] points to first byte past the
+ * RPC-over-RDMA header. For RDMA_MSG, this is the RPC message.
+ *
+ * The length of the RPC-over-RDMA header is returned.
+ *
+ * Assumptions:
+ * - The transport header is entirely contained in the head iovec.
+ */
+static int svc_rdma_xdr_decode_req(struct xdr_buf *rq_arg,
+				   struct svc_rdma_recv_ctxt *rctxt)
+{
+	__be32 *p, *rdma_argp;
+	unsigned int hdr_len;
+
+	rdma_argp = rq_arg->head[0].iov_base;
+	xdr_init_decode(&rctxt->rc_stream, rq_arg, rdma_argp, NULL);
+
+	p = xdr_inline_decode(&rctxt->rc_stream,
+			      rpcrdma_fixed_maxsz * sizeof(*p));
+	if (unlikely(!p))
+		goto out_short;
+	p++;
+	if (*p != rpcrdma_version)
+		goto out_version;
+	p += 2;
+	switch (*p) {
+	case rdma_msg:
+		break;
+	case rdma_nomsg:
+		break;
+	case rdma_done:
+		goto out_drop;
+	case rdma_error:
+		goto out_drop;
+	default:
+		goto out_proc;
+	}
+
+	if (!xdr_check_read_list(rctxt))
+		goto out_inval;
+	if (!xdr_check_write_list(rctxt))
+		goto out_inval;
+	if (!xdr_check_reply_chunk(rctxt))
+		goto out_inval;
+
+	rq_arg->head[0].iov_base = rctxt->rc_stream.p;
+	hdr_len = xdr_stream_pos(&rctxt->rc_stream);
+	rq_arg->head[0].iov_len -= hdr_len;
+	rq_arg->len -= hdr_len;
+	trace_svcrdma_decode_rqst(rctxt, rdma_argp, hdr_len);
+	return hdr_len;
+
+out_short:
+	trace_svcrdma_decode_short_err(rctxt, rq_arg->len);
+	return -EINVAL;
+
+out_version:
+	trace_svcrdma_decode_badvers_err(rctxt, rdma_argp);
+	return -EPROTONOSUPPORT;
+
+out_drop:
+	trace_svcrdma_decode_drop_err(rctxt, rdma_argp);
+	return 0;
+
+out_proc:
+	trace_svcrdma_decode_badproc_err(rctxt, rdma_argp);
+	return -EINVAL;
+
+out_inval:
+	trace_svcrdma_decode_parse_err(rctxt, rdma_argp);
+	return -EINVAL;
+}
+
+static void rdma_read_complete(struct svc_rqst *rqstp,
+			       struct svc_rdma_recv_ctxt *head)
+{
+	int page_no;
+
+	/* Move Read chunk pages to rqstp so that they will be released
+	 * when svc_process is done with them.
+	 */
+	for (page_no = 0; page_no < head->rc_page_count; page_no++) {
+		put_page(rqstp->rq_pages[page_no]);
+		rqstp->rq_pages[page_no] = head->rc_pages[page_no];
+	}
+	head->rc_page_count = 0;
+
+	/* Point rq_arg.pages past header */
+	rqstp->rq_arg.pages = &rqstp->rq_pages[head->rc_hdr_count];
+	rqstp->rq_arg.page_len = head->rc_arg.page_len;
+
+	/* rq_respages starts after the last arg page */
+	rqstp->rq_respages = &rqstp->rq_pages[page_no];
+	rqstp->rq_next_page = rqstp->rq_respages + 1;
+
+	/* Rebuild rq_arg head and tail. */
+	rqstp->rq_arg.head[0] = head->rc_arg.head[0];
+	rqstp->rq_arg.tail[0] = head->rc_arg.tail[0];
+	rqstp->rq_arg.len = head->rc_arg.len;
+	rqstp->rq_arg.buflen = head->rc_arg.buflen;
+}
+
+static void svc_rdma_send_error(struct svcxprt_rdma *rdma,
+				struct svc_rdma_recv_ctxt *rctxt,
+				int status)
+{
+	struct svc_rdma_send_ctxt *sctxt;
+
+	sctxt = svc_rdma_send_ctxt_get(rdma);
+	if (!sctxt)
+		return;
+	svc_rdma_send_error_msg(rdma, sctxt, rctxt, status);
+}
+
+/* By convention, backchannel calls arrive via rdma_msg type
+ * messages, and never populate the chunk lists. This makes
+ * the RPC/RDMA header small and fixed in size, so it is
+ * straightforward to check the RPC header's direction field.
+ */
+static bool svc_rdma_is_backchannel_reply(struct svc_xprt *xprt,
+					  __be32 *rdma_resp)
+{
+	__be32 *p;
+
+	if (!xprt->xpt_bc_xprt)
+		return false;
+
+	p = rdma_resp + 3;
+	if (*p++ != rdma_msg)
+		return false;
+
+	if (*p++ != xdr_zero)
+		return false;
+	if (*p++ != xdr_zero)
+		return false;
+	if (*p++ != xdr_zero)
+		return false;
+
+	/* XID sanity */
+	if (*p++ != *rdma_resp)
+		return false;
+	/* call direction */
+	if (*p == cpu_to_be32(RPC_CALL))
+		return false;
+
+	return true;
+}
+
+/**
+ * svc_rdma_recvfrom - Receive an RPC call
+ * @rqstp: request structure into which to receive an RPC Call
+ *
+ * Returns:
+ *	The positive number of bytes in the RPC Call message,
+ *	%0 if there were no Calls ready to return,
+ *	%-EINVAL if the Read chunk data is too large,
+ *	%-ENOMEM if rdma_rw context pool was exhausted,
+ *	%-ENOTCONN if posting failed (connection is lost),
+ *	%-EIO if rdma_rw initialization failed (DMA mapping, etc).
+ *
+ * Called in a loop when XPT_DATA is set. XPT_DATA is cleared only
+ * when there are no remaining ctxt's to process.
+ *
+ * The next ctxt is removed from the "receive" lists.
+ *
+ * - If the ctxt completes a Read, then finish assembling the Call
+ *   message and return the number of bytes in the message.
+ *
+ * - If the ctxt completes a Receive, then construct the Call
+ *   message from the contents of the Receive buffer.
+ *
+ *   - If there are no Read chunks in this message, then finish
+ *     assembling the Call message and return the number of bytes
+ *     in the message.
+ *
+ *   - If there are Read chunks in this message, post Read WRs to
+ *     pull that payload and return 0.
+ */
+int svc_rdma_recvfrom(struct svc_rqst *rqstp)
+{
+	struct svc_xprt *xprt = rqstp->rq_xprt;
+	struct svcxprt_rdma *rdma_xprt =
+		container_of(xprt, struct svcxprt_rdma, sc_xprt);
+	struct svc_rdma_recv_ctxt *ctxt;
+	__be32 *p;
+	int ret;
+
+	rqstp->rq_xprt_ctxt = NULL;
+
+	spin_lock(&rdma_xprt->sc_rq_dto_lock);
+	ctxt = svc_rdma_next_recv_ctxt(&rdma_xprt->sc_read_complete_q);
+	if (ctxt) {
+		list_del(&ctxt->rc_list);
+		spin_unlock(&rdma_xprt->sc_rq_dto_lock);
+		rdma_read_complete(rqstp, ctxt);
+		goto complete;
+	}
+	ctxt = svc_rdma_next_recv_ctxt(&rdma_xprt->sc_rq_dto_q);
+	if (!ctxt) {
+		/* No new incoming requests, terminate the loop */
+		clear_bit(XPT_DATA, &xprt->xpt_flags);
+		spin_unlock(&rdma_xprt->sc_rq_dto_lock);
+		return 0;
+	}
+	list_del(&ctxt->rc_list);
+	spin_unlock(&rdma_xprt->sc_rq_dto_lock);
+
+	atomic_inc(&rdma_stat_recv);
+
+	svc_rdma_build_arg_xdr(rqstp, ctxt);
+
+	/* Prevent svc_xprt_release from releasing pages in rq_pages
+	 * if we return 0 or an error.
+	 */
+	rqstp->rq_respages = rqstp->rq_pages;
+	rqstp->rq_next_page = rqstp->rq_respages;
+
+	p = (__be32 *)rqstp->rq_arg.head[0].iov_base;
+	ret = svc_rdma_xdr_decode_req(&rqstp->rq_arg, ctxt);
+	if (ret < 0)
+		goto out_err;
+	if (ret == 0)
+		goto out_drop;
+	rqstp->rq_xprt_hlen = ret;
+
+	if (svc_rdma_is_backchannel_reply(xprt, p))
+		goto out_backchannel;
+
+	svc_rdma_get_inv_rkey(rdma_xprt, ctxt);
+
+	p += rpcrdma_fixed_maxsz;
+	if (*p != xdr_zero)
+		goto out_readchunk;
+
+complete:
+	rqstp->rq_xprt_ctxt = ctxt;
+	rqstp->rq_prot = IPPROTO_MAX;
+	svc_xprt_copy_addrs(rqstp, xprt);
+	return rqstp->rq_arg.len;
+
+out_readchunk:
+	ret = svc_rdma_recv_read_chunk(rdma_xprt, rqstp, ctxt, p);
+	if (ret < 0)
+		goto out_postfail;
+	return 0;
+
+out_err:
+	svc_rdma_send_error(rdma_xprt, ctxt, ret);
+	svc_rdma_recv_ctxt_put(rdma_xprt, ctxt);
+	return 0;
+
+out_postfail:
+	if (ret == -EINVAL)
+		svc_rdma_send_error(rdma_xprt, ctxt, ret);
+	svc_rdma_recv_ctxt_put(rdma_xprt, ctxt);
+	return ret;
+
+out_backchannel:
+	svc_rdma_handle_bc_reply(rqstp, ctxt);
+out_drop:
+	svc_rdma_recv_ctxt_put(rdma_xprt, ctxt);
+	return 0;
+}